GENERAL39876 - Laserfiche WebLink

Home Browse Search

-32- Waste-Rock Piles No ground water contamination is expected from the waste rock piles. The initial waste rock pile and the larger life-of-mine pile are both designed to handle the worst case condition, that is to handle toxic, acidic, alkaline, and/or combustible waste rock. (See Geo-Hydro Report dated March, 1981). The initial waste rock pile will be situated over 35 to 75 feet of "impervious clay soils" to prevent leachate from migrating to the ground water table which lies in excess of 50 feet below the surface. The monitor wells 40 feet to 60 feet in depth are to be installed to assess any impacts on the ground water. The location of these monitoring wells has been provided in the application. Mt. Gunnison has and will continue to monitor these wells to identify any impact from the pile. Effects of Mining on Surface Water The Mt. Gunnison No. 1 Mine plan is designed to minimize the impacts of the project on the surface water hydrology of the region. Disturbed area drainage is collected and treated on the site. Drainage from undisturbed land is diverted around the site. Six sedimentation ponds have been proposed for the surface facilities area. A system of lined ditches will convey waters from the disturbed areas to the ponds. All six sedimentation ponds would discharge into the North Fork. The mine operation has obtained the appropriate NPDES permits. Effluent quality for the sedimentation ponds has been monitored to determine permit compliance. The applicant will also continue monitoring surface waters to determine the impact of mining on the hydrologic regime. Runoff from the waste disposal sites would be routed through the sediment control system and must meet effluent limitations. Final design for the waste rock piles, which would include a surface drainage system, has not been determined. Analysis of sample rock provided by WECC indicates that potential toxicity levels are below EPA standards. Consequently, it appears that if runoff were to develop from the waste piles, minimal impact will occur on the North Fork of the Gunnison River. Mt. Gunnison will be monitoring both ground water quality under the pile, leachate quality from the subdrains, and spring quality from the base of the permanent pile site when constructed. WECC estimates that treated waste water will be 38,000 gallons per day (gpd). Since secondary treatment will occur, the concentrations of BOD, COD, TSS, nitrogen, phosphorus, and so forth of the North Fork of the Gunnison River may experience alteration. However, for February, the minimal flow of the river is about 63 CFS, thus, the addition of 38,000 gpd (or 0.0589 CFS) of treated effluent will have minimal impact. It is anticipated that the five mines listed above will contribute much less than 38,000 gpd to the river. Consequently, assuming each provides secondary treatment, it is not expected that any major degradation of water quality to the North Fork of the Gunnison River will occur.